1. Field of the Invention
The present invention relates to a high-brightness planar lighting device using a laser light source used for a non-self-luminous display device such as a liquid crystal television, and to a liquid crystal display device using the high-brightness planar lighting device.
2. Description of the Background Art
A liquid crystal display device displays an image by controlling the amount of transmission of the light illuminated from the back side, using the electro-optic effect due to the orientation of liquid crystal molecules. Accordingly, the liquid crystal display device requires a planar lighting device referred to as a backlight unit generally including a vacuum fluorescent display and the like. In recent years, the screen of such a liquid crystal display device increases in size, and even a display device for a more than 50-inch size television is in practical use.
However, since with the increase in size, the power consumption also increases, there is a need for technological development for the realization of low power consumption. At the same time, there is also a need for an increase in light-and-shade contrast so as to improve image quality, a need for structural simplification and ease of mass production so as to reduce cost, and the like.
Of the above needs, in response to the realization of low power consumption, the use of a light-emitting diode or a laser, each having high luminous efficiency, as a light source is considered, and a planar lighting device using a light-emitting diode as a light source is even in practical use already.
For example, Japanese Laid-Open Patent Publication No. 2004-226709 (Patent Document 1) discloses a planar lighting device for, by using a light-guiding sheet that includes a substrate on the whole surface of which successive tubular light guides are arranged and thus devising the formation positions of a plurality of light-emitting openings for emitting a light from the tubular light guides, making approximately uniform the intensity of the light emitted from the whole surface of the substrate. The light emitted from a light source is incident on the end of each tubular light guide, propagates within the tubular light guide while multiple reflected therefrom, and is emitted from the plurality of light-emitting openings formed on the surface of the tubular light guide. The plurality of light-emitting openings are arranged such that the farther from the end, the higher the layout density or the light-emitting opening area rate. Based on this structure, Patent Document 1 realizes a light intensity that requires low power consumption and is uniform.
Further, Japanese Laid-Open Patent Publication No. 2006-134720 (Patent Document 2) discloses a planar lighting device for, by using an optical waveguide arranged in contact with a light-guiding plate and bent multiple times, making approximately uniform the intensity of the light emitted from the light-guiding plate. The light emitted from a light source is incident on the end of the optical waveguide, propagates within the optical waveguide while multiple reflected therefrom, is reflected from a reflection surface within the optical waveguide, and is emitted to the light-guiding plate that contacts the optical waveguide. Based on this structure, Patent Document 2 realizes a light intensity that requires low power consumption and is uniform.
The conventional planar lighting device disclosed in Patent Document 1 is devised such that the farther from the end, the narrower the interval between the light-emitting openings, so as to make the intensity of the emitted light uniform.
Further, the conventional planar lighting device disclosed in Patent Document 2 is devised such that the light propagating within the tubular optical waveguide is reflected from the reflection surface and is emitted, so as to make the intensity of the emitted light uniform.
However, the above-devised structures complicate the designs of the light guides and the optical waveguide, and thus become a cause of increasing the costs of producing the light guides and the optical waveguide.